Production of silicon.



anonce o. serrano, or Eas'r cannon,

concs nooit, VIRGINIA,assumons To ATER@ onirica.

NEW JEEsEY. AM) rnANZ VON KUGELGEN, or Hoi.-

YORK. Y.,1\ (.ORPOlLTlN Ol NEW YORK.

PB. UCTIGN OF SLXCON.

Specification of Letters Patent.

Patented March so, 1909.

Application filed 'ay le, 1907. Serial No. 373,629..

To als.' whom in' may conca/"n:

15e 1t. known that we (insonni-1 O. t:\,1=.\\.\un7 a citizen ot the United States. residing` in hast Orange, in the county of Essex and "v 1- v T 1 btatc or .hcw Jersey, and humm vox KoEiamN, a subject of the German Eni-- residingY 1n Holcombs Roel', in the.;` county ot Bcdtord and ttate ot Vlre'inimf powdered carbon in a carbon cylinder and obtained a mixture of silicon and lsiliconcarbid, the latter predominating. Moissan stated that hy cooling the silicon vapor 4at the moment of production, this process might he applied nto the. preparation of silicon but suggested no way oit accomplishing this result. Bernard Scheid has proposed to add an alkaline silicateto the mixture of silica and carbon in the electric furnace and to absorb the silicon producethat the moment of its formation, by lthe melted silicate so that it is protected from v'olatilizatiorn his idea being` that the silicon vapor asitI is evolved gets outside the range ofthe electrode or the luminous arc and iscondensed ant taken up by the liquidmelted silicate surrounding it. (U. i

S. Patent No. (362.548.) Tone uses linie or iiuorspar as the flux; to form a molten' silicate, `which he. u as a resistance conductor, laying stress u'poi. the idea that the electric are is unsuitable t'or producing silicon. (Uf S. Pat. No. 84l2f273). Tone has also proppsetl. to produce metallic silicon by heating' silica and carbon in an incandescent electric furnace keeping the temperature below the limits at which Yoiatilination occurs.7 (li. S. Patent No. 'Tet-5,122).

Vv' e laure-found that the use ot' iuxes in the sineltinr ot' a mixture ot silica and carbon is undesirzhle und tends to deleat the. object sought, probably because it lowers the melting point of the i and, partlyv at least.y substitutes the lliuid rc ist-ance ot the silicate .For the sistance ot the ordinarj, arc.

ive consider that the high tenuierature of the. gaseous electric arc can lit-tier he utilfoutents of the furnace gaseous reiz/.ed for the production of silicon than a iiuid resistance or a partlyY tluid partly gascousl resist-nice, and therefore dispense entirol;v with the use of fluxes (in tact carei full).v avoiding them) and prevent the loss ot silicon by rolatilization in quite a different manner.

substantially pure silica and a carbona'ceoiis4 reducingr agent, preferably pure colte. and subject. a mixture thereotl to the heatI of a powerful electric arc. Ylt' arhon is used as reducingl agent.r the reaction is Si02+20=si+200- Vlt silicon carbid is used as reducing` agent,

the reaction is in which latter reaction it is probable that the Si() is first decomposed and the carbon (in the form ot' graphite) then reduces the SiO..

in practicing our invention We preferably use a double-pole arc furnace with substantiall;r vertical carbon electrodes.

rhe accompanying drawing is a vertical section ot' a suitable construction of furnace.

{eten-ring to the drawing, let. A represent.

the body or crucible of the 'furnace whichis nir-.de of or lined with silica sand.

.l is the hearth which may be made oi' carbon. A Ag v C C are the electrodes.y being parallel upright pencilsI (it carbon or graphite which are carried in suitable holders D D which are connected with the oppositeterminals of a dynamo or other generator l" is the furnace top which is shown l the mittag-cooled type, and HH are watercooled insulated bushings through which the pencils pass.

isa tap hole. i

Vithin the furnace is 'shown a molten bath@r or" reduced silicon, and above this and surroundingg;I the pencils is the powdered mixture of silicon and carbon.

and lou' voltage, an arc of 15,000 amperes at 2l() volts heingsafely maintained by an electrode ofi about four square feet cross section.

We t'eed into such a .furnace a coarsely Ve use a `silicon compoundT preferably a as of lle prefer to use an arc of hiffh am )crave 4 ground mixture of ii'a't rock and carbon,

preferably merely crushing the dint rock to about .l inch mesh and grinding the colte so lthat it shall pass al() mesh screen. Sticha mixture is very porous and assists in obtaining the conditions, we shall presently describl. rihe mixture is kept preferably piled about eighteen inches above the lower end of' thc electrode, so that the are is maintained in the midst of the mass of porous mixture. lV e prefer to start with a charge made up oi about T5 parts by weight of flint rock to oi colte, so as to introduce a surplus-of silica.,l afterward changing this to 70 parts ot' li'nty rock to 30 of coke. It will be observed that there is no excess ot' carbon, or barely enough to maintain a reducing atmosphere around the incandescent zone 0I" the are. rllhe temperature maintained under these conditions is above that at which silicon carbid remains stable so that, even if this material is formed in part, it is immediately decomilioscd/ The silicon is reduced in the torni of Ya por and expands into the interstices of the porous mixture, where it condenses. These interstices being full of a reducing gas, namely C0, allow the silicon to condense without being orti-v dized.' The reduced' silicon percolatesvdown through the porous mass and collects at the bottom of the Crucible. it is tapped out ln'to carbon molds from time to time. i el therefore, in practicing this invention, maintain a reduction zone high that silicon carbid cannot form or, if formed in part. is decomposed; around this zone ot" reduction we maintain a cooler porous condensing zone, the interstices of which we keep filled with a reducing atmosphere which prevents the vapor of sili-` con from oxidizing before it can condense. The importance of this reducing at'lnosphere in the interstices of the porous condensing zone is strongly shown when the escaping mixture and allow some air to enter. Immediately the -silicon vapor oxidizes and .spurts out: of the hole in dense clouds of rlie molten silicon may j Witness amorphous silica.

be tapped out into the open air, the temperaat a temperature so.

reduction blow a hole in the l i l l ture being too low to cause it to re-oXidizc.

' signed our names in the crepes" oxidizing atmosphere in which the volatili ized silicon is condensed.

2. The process oi producing silicon by subjecting silica anda carbonaceous reducing agent to sutlicicnt heat to reduce said com pound and Yolatilize the silicon, while maintaining around or above the zone of reduction a cooler zone containingr a non-oxidizing atmosphere in which tin silicon vapor is condensed.

The process of producing silicon by subjecting a suitable silicon compound and a carlwnaceous reducing agent in an electric. furnace to a temperature above that at which silicon carbid remains stable, thereby reducing the silicon compound and forming silicon i'apor. while maintaining around or above the zone of reduction a cooler zone containing' a non-oxidizing atmosphere in `which the silicon vapor is condensed.

i. The process of producing silicon by subjecting a porous mixture of silica and carbon to the heat of an electric arc, said mixture is reduced and the silicon is Yolatilized, While maintaining the are deeply buried under such mixture, whereby a cooler zone is maintained around the zone of reduction in which the silicon vapor is condensed.

In witness whereof, we have hereunto presence of two subscribing witnesses.

GEORGE O. SEFVARD. FRANZ VON KGELGEN.

F. vorY BniLnR. Hmm RILEY Lne.

whereby f 

